The present invention relates to a method of mounting an IC (integrated circuit) chip for a thin-film magnetic head element used for a magnetic disk device, for example, and to a method of manufacturing a head suspension assembly (HSA) with the IC chip.
In a magnetic disk device, a thin-film magnetic head element for writing magnetic information into and/or reading magnetic information from a magnetic disk is, in general, formed on a magnetic head slider flying in operation above the rotating magnetic disk. The slider is supported by a suspension made of a resilient thin metal plate extended from one end of each movable arm of the magnetic disk device.
Recently, recording frequencies in the magnetic disk have rapidly increased to satisfy the requirement for ever increasing data storage capacities and densities in today""s magnetic disk devices. In order to realize higher frequency recording, an HSA structure has been proposed with a suspension for supporting both a magnetic head slider and a drive IC chip of a driver circuit for the magnetic head element. According to this structure, because the length of trace conductors from the driver circuit to the magnetic head element can be shortened, generation of undesirable noise from the trace conductors can be effectively suppressed, resulting in improved high frequency recording characteristics.
Such an IC chip may be, however, heated to a high temperature as a result of the writing current flowing through it during recording operations. In order to cool the heated IC chip by air flowing produced by the rotating magnetic disk, the IC chip will be mounted on a surface of the suspension, which counters the magnetic disk surface in operation.
The HSA with the IC chip will have a greater thickness increased by the mounting height of the IC chip. Generally, in the magnetic disk device, in order to increase the record capacity per magnetic disk, both sides of the disk are used for recording, and in addition, a plurality of such the magnetic disks are axially mounted. Therefore, two HSAs for writing/reading magnetic information will exist between the two magnetic disks, and, thus, the whole thickness of the magnetic disk device equipped with the HSAs with IC chips becomes great. This large thickness of the magnetic disk device will become a big problem particularly when the magnetic disk device is mounted in a thin notebook type personal computer.
Therefore, it is required for such an IC chip to be fabricated to be thinner than a general-purpose IC chip. Namely, the general-purpose IC chip has a thickness of about 0.3-0.4 mm, whereas the IC chip for the thin-film magnetic head has a thickness less than 0.25 mm, preferably a thickness of about 0.12 mm.
The C4 (Controlled Collapse Chip Connection) process is a typical process for mounting such an IC chip on a suspension. In the C4 process, first, flux for solder material is applied to bump balls of the IC chip and then the IC chip is bonded to connection pads by reflow head bonding.
If the mounting of the IC chip is performed by the reflow soldering using flux, it is necessary to execute the cleaning process after bonding. Namely, int eh C4 bonding process, flux is applied to the suspension at a position to which the IC chip is bonded, in order to promote melting of the solder and to temporarily adhere the IC chip to the suspension during reflow soldering. Because the applied flux may have adverse effect of producing gas, for example, the cleaning has to be done after bonding.
This cleaning process will exert an influence upon the suspension. Namely, although high accuracy is required in a bending angle of the suspension, this bending angle may unintentionally change during the cleaning process. Thus, it is difficult to use the C4 process in the mounting of the IC chip on the suspension.
An ultrasonic bonding can be carried out without executing the cleaning process. In the ultrasonic bonding process, no solder bump is used but gold (Au) bumps formed on the IC chip are used. Namely, bonding is executed by applying an appropriate pressure and ultrasonic vibration to the Au bumps that are contacting with the respective Au pads on the suspension so as to fuse the Au. Because no soldering flux is utilized in this ultrasonic bonding process, no cleaning process is necessary.
However, if a heavy load and great ultrasonic power are applied to the very thin and small IC chip for the thin-film magnetic head element in order to mount it in the ultrasonic bonding process, damage such as scratches or cracks may be produced on the IC chip surface.
Even if few defects such as scratches or cracks arise on the IC chip surface, a silicon particle may fall from this IC chip. This is never allowed in the magnetic disk device. Namely, in the magnetic disk device, generally, because the magnetic head slider flies at extremely low height above the rotating disk for performing reading/writing operations, no dust is allowed to exist. Thus, it is very difficult to determine the conditions for mounting the IC chip using the ultrasonic bonding process.
It is therefore an object of the present invention to provide a method of mounting an IC chip and a method of manufacturing a HSA with the IC chip, whereby no damage occurs on a body of the IC chip even if the IC chip is very thin and very small.
According to the present invention, a method of mounting an IC chip on a suspension is provided. The suspension has connection pads, and the IC chip has a circuit for a thin-film magnetic head element and connection terminals connected to the circuit. The mounting method includes a step of increasing a load applied to the IC chip so that metal bumps formed on the connection terminals press the connection pads formed on the suspension, respectively, and a step of starting application of ultrasonic vibration to the IC chip during the increasing of the load applied to the IC chip.
Also, according to the present invention, a method of manufacturing an HSA with a suspension and an IC chip is provided. The suspension has connection pads, and the IC chip has a circuit for a thin-film magnetic head element and connection terminals connected to the circuit. The manufacturing method includes a step of forming metal bumps on the connection terminals, a step of positioning the IC chip so that the metal bumps oppose to the connection pads formed on the suspension, respectively, a step of increasing a load applied to the IC chip so that the metal bumps press the connection pads formed on the suspension, and a step of starting application of ultrasonic vibration to the IC chip during the increasing of the load applied to the IC chip to mount the IC chip on the suspension.
If the application of the ultrasonic vibration is started while the load applied to the IC chip is increasing, top ends of the metal bumps, which have a convex shape, are softened by the ultrasonic vibration, and are pushed by the applied load against the connection pads of the suspension. Also, this load applied to the IC chip is increasing. Thus, the metal bumps are bonded with the connection pads by means of melting and crushing their top ends. As a result, although the IC chip for the thin film magnetic head element is very thin and very small, sufficient mounting intensity can be obtained without applying an unnecessarily large load to the body of the IC chip.
In other words, according to the present invention, the ultrasonic bonding can be performed without generating damage on the surface of the IC chip. Even if the IC chip is very thin and small, because the mounting is possible under the lower ultrasonic power and load, a decrease of inspection items at the time of actual fabrication and an improvement in quality can be expected. Therefore, the productivity can be greatly improved.
It is preferable that the load is increased to a predetermined value, kept at a predetermined value for a predetermined period of time, and then decreased.
It is also preferable that the load is increased to a first predetermined value, kept at the first predetermined value for a first predetermined period of time, increased to a second predetermined value, kept at the second predetermined value for a second predetermined period of time, and then decreased.
It is preferable that the application of ultrasonic vibration to the IC chip is finished during the application of the load of the IC chip.
It is further preferable that the application of the ultrasonic vibration to the IC chip is finished during the increasing of the load applied to the IC chip.
Preferably, the metal bumps are gold bumps or copper bumps. Also, preferably, the connection pads are made of gold or copper.
It is preferable that the suspension is fabricated by forming a trace conductor member and the connection pads connected to the trace conductor member on a resilient flexure, and by fixing the flexure to a resilient load beam.
Further objects and advantages of the present invention will be apparent from the following description of the preferred embodiments of the invention as illustrated in the accompanying drawings.